P0128
P0128Component Location:
General Description
When the engine is first started, the fuel control system operates in an open loop operation, ignoring the HO2S (Heated Oxygen Sensor) signal and calculating the air/fuel ratio based on inputs from the engine coolant temperature, the throttle position and the mass air flow sensors. The PCM will begin by using the oxygen sensor signal for controlling the fuel delivery (closed loop) when the following conditions are met:
- The engine has run a minimum amount of time at engine start up.
- The HO2S has a varying voltage output showing that it is hot enough to operate properly.
- The ECT has increased a minimum amount based on the ECT at start up.
The PCM monitors the amount of time for the cooling system to achieve closed loop operating temperature. The engine coolant temperature sufficient to allow closed loop operation is not achieved within a predetermined time frame, PCM sets DTC.
DTC Description
If the engine coolant temperature does not reach the specified value within the allocated period of time, the PCM determines that a malfunction exists and a DTC is stored. MIL (Malfunction Indication Lamp) turns on when the malfunction lasts till consecutive 2 driving cycle.
DTC Detecting Condition:
Schematic Diagram:
Signal Waveform:
Monitor Scantool Data
1. Engine "OFF"
2. Monitor Engine Coolant Temperature Sensor parameter on Current data
3. Is the measured ECTS parameter displayed within specifications?
YES - Fault is intermittent caused by poor contact in the sensor's and/or PCM's connector or was repaired and PCM memory was not cleared. Thoroughly check connectors for looseness, poor connection, bending, corrosion, contamination, deterioration, or damage. Repair or replace as necessary and go to "Verification of Vehicle Repair" procedure
NO - Go to "Component Inspection" procedure
Component Inspection
1. Check Thermostat
1. Check cooling system coolant level and fill if low.
2. Check for a proper cooling system operation. Especially check that cooling and condenser fan working normally.
3. Remove the thermostat and check the following items:
1. Stuck or damaged
2. Verify the temperature at which the valve is open: 80 - 84 °C (176 - 183.2 °F)
4. Has a problem been found?
YES - Substitute with a known - good Thermostat and check for proper operation. If the problem is corrected, replace Thermostat and go to "Verification of Vehicle Repair" procedure.
NO - Substitute with a known - good PCM and check for proper operation. If the problem is corrected, replace PCM and go to "Verification of Vehicle Repair" procedure.
CAUTION: There is a memory reset function on scantool that can erase optional parts automatically detected and memorized by PCM. Before or after testing PCM on the vehicle, use this function to reuse the PCM on the others.
Verification of Vehicle Repair
After a repair, it is essential to verify that the fault has been corrected.
1. Monitor and record the Freeze Frame Data for the Diagnostic Trouble Code (DTC) which has been diagnosed.
2. Using a Scantool, Clear the DTCs
3. Operate the vehicle within conditions noted in the freeze frame data or enable conditions
4. Monitor that all readiness test have been verified as "Complete"
5. Are any DTCs present?
YES - Go to the applicable troubleshooting procedure.
NO - System is performing to specification at this time.